[llvm] [InstCombine] Don't convert a compare+select into a minnum/maxnum intrinsic that can't be lowered back to a compare+select (PR #177821)

[Sergey Shcherbinin via llvm-commits]

SergeyShch01 wrote:

> As far as I can tell, we haven't. We're just not doing it because the compiler thinks branches are slower.

select-optimize pass which converts selects to branches doesn't work w/ maxnum. Then the compiler doesn't try branches if we substitute select by maxnum and we lose the optimization opportunity.

https://github.com/llvm/llvm-project/pull/177821